We performed a family study of 39 individuals with proven manic-depressive disorder. Among the affected first-degree relatives of these probands, an overall parity of the male-female ratio was found. In addition, there were four instances of father-son transmission of affective illness involving probands of the sample.

These results suggest that any gene locus that exists on the X chromosome is not of itself a sufficient or necessary condition for the transmission of manic-depressive illness. Hence, any implication that X linkage is the primary mode of transmission in manic-depressive illness is premature.